The pathological classification of human mammary carcinoma: past, present and future.

The current classification of mammary carcinoma combines pathological and clinical information in order to define prognostically significant categories. Basic structural features are the anatomic unit of origin, either duct or terminal duct-lobule complex, and the presence or absence of invasion. Approximately 90 percent of carcinomas appear to arise from ducts. About one-fifth of invasive duct carcinomas have a better than average prognosis and distinct light microscopic structural patterns. Future study of biochemical markers may permit further refinement of the existing classification of breast carcinoma and lead to the identification of new prognostically significant categories in the heterogeneous group currently referred to as "ordinary" infiltrating duct carcinoma. However, a conservative approach should be adopted toward altering or abandoning the existing classification of breast carcinoma on the basis of immunocytochemical studies until there is an adequate opportunity to determine which, if any, markers are truly clinically relevant.